The aerodynamic characteristics of wind turbine blades are essential to wind turbine performance. During cold seasons and in cold climates, the outer surfaces of the blades are exposed to ice formation. The accumulation of ice, particularly on the leading edge area, has negative and even substantial effects on the aerodynamic qualities of the blade, since it affects not only the energy performance of the wind turbine but also rotor structural loads by generating vibrations and imbalance in a running wind turbine, and consequently greater wear on components. Extreme ice accumulation, could even cause a forced shutdown, since the blades on a rotor, normally three, must be balanced in terms of weight and, therefore, if ice accumulation compromises the integrity of this balance, the wind turbine must stop to prevent damages caused by imbalance in the mechanical part of the wind turbine. The significant speed and height of the iced blades likewise entails a danger as chunks of ice already formed on the blades could detach and fall at an elevated speed.
A diversity of systems have been conceived to deal with the formation of ice on wind turbine blades such as active and passive ice-resistant and de-icing systems.
One passive ice-resistant system entails coating the blades with ice-resistant paint such as a fluoroethane-based black paint to absorb thermal energy during the day and release it at night, thus heating the blade surface and contributing to the prevention of ice formation to a certain degree. However, the effectiveness of paints of this sort is extremely limited, particularly in very cold climates or on very short winter days.
Hydrophobes are another type of ice-resistant paints. They block water adhesion to the blade surface and, consequently, preclude ice formation. This sort of paint, however, tends to become porous over time, losing its hydrophobic properties, and thus requires reconditioning after a given period, resulting in high costs not only due to the short useful service life but also because the wind turbine must shut down during the corresponding work. Moreover, an increase in hydrophobicity leads to a reduction in adhesion forces, which could result in paint adhesion issues on the blade surface.
Ice-resistant paints for wind turbine blades are described, for instance, in ES2230913T3 and GB2463675A.
Further, high solid paints (“HS Paints”) are also commonly used to paint wind turbine blades. HS paints have two components, namely a polyurethane-based primer, i.e., mixtures essentially comprising synthetic polyurethane resins, organic solvents and pigments, with a content in solids >70% by mass, low density (1.2-1.4 g/cm3), and a content in volatile organic compounds (VOC)<300 g/l; and a second isocyanate-based hardener component that mixes with the primer component before painting the blades. Paints obtained in this manner are cured and dried in the open air, and create coatings that satisfy the strictest requirements regarding the stability of gloss and color, even in extreme climates. They are also highly elastic, resistant to weather and abrasion caused by, for instance, wind and/or rain, scratches, solvents, agents, hydraulic oils, etc., and are thus widely employed in paints used for coating wind turbine blades. Nonetheless, the hydrophobic properties of these paints are limited, and they are thus ineffective against the formation of ice.
Such high solid paints are sold on the market by, for example, the German companies BASF COATINGS GMBH (RELEST® line) and MANKIEWICZ GEBR. & CO. (ALEXIT® line).
It would thus be desirable to obtain a paint having properties tending to avert the formation of ice on wind turbine blades without compromising the resistance to the physical and chemical agents as conferred by conventional paints employed as wind turbine blade coatings, and particularly resistant to UV radiation and erosion, insofar as erosion caused by particles and rain.